The original, still the best Swimming HUD in Second Life.
New 2.0 version, all the old features improved and more added:
Laze away the afternoon floating around on your back.
If Scuba is your thing - use the zero buoyancy feature to improve your experience.
Dive into the water the inbuilt dive system.
If your Av is Tiny... try out the tinyswimming....
All dives and Swim sets are still user definable/creatable..
Bought another pool? Bought a cheap imitation? No problem - use the 'PrimSwim lite' script (copy and transfer) to make your current water work - or use it to make your own pools/creations.
It's at WaterWorks